In order to suppress vibration and rocking which occur during traveling of a vehicle such as a railway vehicle, a linear actuator is used. Suppressing vibration and rocking in a lateral direction with respect to a traveling direction of a vehicle plays an important role to give passengers a comfortable ride and keep safe traveling conditions. In recent years, the study for suppressing rocking and vibration due to the influence of aerodynamic characteristics at the time of high-speed traveling by active control to keep the vehicle attitude stable has been especially advanced. Further, in general, a linear actuator that is used for prevention of rocking of a railway vehicle is used under a condition in which maintenance, such as frequent exchange, cannot be easily performed. Nevertheless, it is required to maintain the function of the linear actuator stably even when the linear actuator is used under a severe temperature condition in which the temperature variation of the installation and operation environment is large (for example, −20° C. to 60° C.). Further, a linear actuator for suppressing vibration and rocking generated during travelling of a railway vehicle needs to be installed in a limited space between the bogie truck and the vehicle body of the railway vehicle, and hence it is necessary that the size of the linear actuator is reduced to maintain the required stroke.
Patent Literature 1 discloses a linear actuator. The linear actuator includes: a main body of a hollow structure having an open end portion and a closed end portion; a cylinder which is fixed to the closed end portion side in the main body and has an open end at the open end portion side; a linear motion rod which has one end extended from the open end portion of the main body, and a wear ring provided at the outer peripheral section of the other end thereof, and which is accommodated in the cylinder so as to be slidable in the axial direction; and a hollow shaft which is rotatably supported in the main body. The linear actuator is disclosed such that the hollow shaft has a permanent magnet at a part of the outer peripheral surface thereof, such that a winding section provided at a portion of the inner surface of the main body, and the permanent magnet configure a hollow motor, such that a nut section coaxially fixed to the hollow shaft, and a screw section of the outer peripheral surface of the linear motion rod are engaged with each other to form a rotation/linear motion converting mechanism, and such that a rotation oil seal section is provided so as to seal between the hollow shaft and the main body on both axial direction sides of the nut section. Therefore, a compact linear actuator is disclosed in which back drive force is small and, in which sticking due to abrasion powders, or the like, hardly occurs.
Patent Literature 2 discloses an electro-mechanical linear actuator configured such that a nut is rotatably accommodated in a frame, and a hollow motor is configured by a magnet fixed to the outer periphery of the nut, and a coil fixed to the inner periphery of the frame, such that a screw is formed in the nut, and a reverse transfer system-ball screw is configured by the screw, the nut, and a plurality of balls which are disposed between the screw and the nut so as to circulate along a cooperative ball groove forming the path of the balls, and such that a rod fixed to the screw is driven in the axial direction by the rotation of the hollow motor.